Apparatuses and circuits for dimming gaseous discharge devices



Jan. 28, 1958- A. BASTIAN 2,

APPARATUSES AND CIRCUITS FOR DIMMING GASEOUS DISCHARGE DEVICES FiledJune 8, 1954 :57 4 I) INVENTOR.

l'Jnited States Patent Oflice APPARATUSES AND CIRCUITS FOR DIMMINGGASEOUS DISCHARGE DEVICES Arthur L. Bastian, Yonkers, N. Y., assignor toWard Leonard Electric Company, a corporation of New York ApplicationJune 8, 1954, Serial No. 435,170 12 Claims. (Cl. 315-98) This inventionrelates to electrical circuits operating gaseous discharge devices suchas fluorescent lamps and particularly to circuits for adjusting theintensity of illumination of the lamp.

Electrical discharge lamps, such as fluorescent lamps, contain ionizablegas which presents a high impedance when the gases are substantiallyun-ionized and a low impedance when the gases are ionized. A highvoltage is required across the electrodes of the lamp to cause the gasesto ionize. Once .the gases have ionized the voltage required to forcethe electrons through the gas is substantially lowered and as thecurrent increases the impedance of the tube generally decreases sincewith more current more ions are formed and the conductivity of the tubeincreases. The current is limited by the external circuit. The intensityof the illumination of the phosphoric coating is dependent of the energyimpressed on the electrodes since the voltage of the lamp across thelamp electrodes is substantially constant during ionization. Theintensity of illumination is controlled by the amount of currentsupplied to the lamp. As the current decreases the intensity ofillumination decreases and as the current increases the intensity ofillumination increases. The difliculty encountered in operating a lampat low intensities with conventional ballasts is that it becomesunstable and will deionize and the arc becomes extinguished. In reducingthe current supplied to the lamp the intensity of illumination is slowlyreduced but before there is a substantial reduction in brilliance of thelamp the arc is extinguished. Correlative with this is that the lampcannot be started at the low intensity levels.

The circuits controlling such lamps should provide a high voltage toforce current through the high impedance and provide a means to limitthe current through the lamp in view of the aforementioned negativeimpedance characteristic of the lamp.

ln changing the intensity of illumination of fluorescent lamps it isdesirable that the illumination may be smoothly and evenly changed fromfull brilliance to dim-out and from dim-out to full brilliance withoutany intermediate conditions of instability or a reversal of change ofillumination. The change should be continuous and uniform throughout theentire range of illumination. It is also desirable that at lowerillumination the lamp remains lit and does not abruptly extinguishitself. Another requirement is that the lamp can be instantaneouslystarted at any degree of illumination. A further desirable requirementis to limit the voltages in the circuit and lamp fixtures to safe valuesso as to prevent undue hazard from electrical shock.

The present invention is applicable to the conventional fluorescent lamphaving a cylindrical glass envelope with a phosphor or fluorescentcoating along the entire length of the inner surface of the envelope andwith heated coated cathodes at each end of the glass envelope. The endsof the envelope are sealed. The envelope contains a gaseous atmospherecomprising a rare gas, such as argon, at a pressure of a few millimetersof mercury and a small quantity of mercury which during the operation ofthe lamp has a low pressure in the order of 6 to 10 microns of mercury.On ionization of the argon and mercury by the application of a voltageacross the heated electrodes the fluorescent coating is excited to emitlight by the radiation from the are through the ionized gases.

An object of this invention is to provide a circuit to vary theintensity of illumination of fluorescent lamps.

Another object of the invention is to provide a circuit to vary theintensity of illumination of fluorescent lamps smoothly and evenlywithout discontinuity over the range of illumination.

Another object of the invention is to provide a circuit for controllingthe illumination of fluorescent lamps that comprises a minimum ofcomponents.

Another object of the invention is to provide a circuit for controllingillumination of fluorescent lamps that is inexpensive and reliable underall conditions of operation.

Another object of the invention is to provide a circuit and apparatusthat varies the intensity of illumination and also starts thefluorescent lamp and limits the arc current therethrough.

A further object of the invention is to provide a circuit forcontrolling the intensity of illumination of fluorescent lamps that willstart the lamp at all degrees of illumination and under all conditionsof operation.

A still further object is to provide a circuit operating at voltagessafe from the hazard of electrical shock that adjust the intensity ofillumination of the lamp.

Other and further objects will appear from the following specificationtaken in connection with the accompanying drawings in which:

Fig. 1 shows a circuit diagram illustrating the invention.

Fig. 2 illustrates a modification of the ballast.

The fluorescent lamp 10 has a sealed cylindrical glass envelope with afluorescent or phosphor coating 12, such as a zinc beryllium silicateand magnesium tungstate mixture, on the inner surface of the envelope.The coating radiates light in a visible spectrum on energization by theradiation from the ionized gas contained within the sealed envelope. Thegas may comprise a rare gas, such as argon, at a pressure of about 3.5mm. of mercury, and a small quantity of mercury at a low pressure of theorder of 6 to 10 microns. Filaments or electrodes 13 and 14 positionedinside of and at a respective end of the glass envelope lit and may beof the oxide coated type, preferably in the form of coiled tungsten wireactivity with alkaline earth metal oxides. In the case of a 48-inchfluorescent lamp the application of a voltage in the order of 300 to 400volts across the electrodes 13, 14 ionized the gases and a current isconducted between the electrodes energizing the gas and causing it toradiate. The radiation of the gas in turn excites the fluorescentcoating which radiates visible light. As an example of a given lamp whenit is conducting, the voltages across the lamp has a range of to voltsand the current through the lamp has a range from .0005 to .5 ampere.

The fluorescent lamp is supplied with an alternating current and voltagethrough autotransformer 15 from terminals 17, 18 connected to a suitablealternating current supply. The current passes through a path providedby the conducting wire 19 connected to the electrode 14 through the lampand from the electrode 13 through the conducting wire 20 through thecoil 21 and Wire 22 to the slider 44 of the transformer 15. The coil 23is connected to the autotransformer 15 by the lines 19 and 24. The coil23 is wound on a magnetic core 26 which comprises legs 27, 28 and 29.The coil 23 is Wound on leg 27 and on passage of current through thecoil 23 provides flux passing through legs 28 and 29. The core 26consists of a laminated ferro-mag- Patented Jan. 28, 1953 netic metal.The leg 28 has an air gap and the leg 29 has small cross-section withhigh permeability at low flux values so that on application of asinusoidal flux to the legs the leg 29 carries the initial fluxes whichsaturate the leg and that the remaining flux is carried by the leg 23.The constricted leg 29 has a higher permeability than the leg 28 with anair gap 30 at the low values of flux created by the coil 23 and becomessaturated at these low fluxes. Thus during the small portion of theperiodic flux cycle generated by coil 23 the greater portion of the fluxpasses through the constricted path of leg 29. During the larger andlonger portion of the periodic flux cycle generated by coil 23 duringwhich the instantaneous flux value is relatively low the greater portionof the flux passes through the path provided by the leg 28 with the gap30. The constricted path provided by the leg 29 is magneticallysaturated and therefore the additional flux must pass through the airgap 30. The leg 29 is magnetically separated from the core 31 so thatthe flux passing through leg 29 J is not shunted around coil 21 throughthe leg 34. The coil 21, conducting the arc current passing through thelamp 10, is Wound around leg 32 of the ferro-magnetic core 31 and theleg 29 of the ferromagnetic core 26. The flux created by the coil 21passes through the legs 32, 33, 34, 35. The elfect of the small amountof flux created by coil 23 passing through the constricted leg 29 andcoupled with the coil 21 is to generate a peak voltage wave in coil 21.A sinusoidal alternating current supplied to the terminals 17, 18. Thepeaked voltage occurs at the maximum value of the voltage. A voltagepeak occurs for each half cycle of all values of current passing throughthe lamp.

The peaked voltage is created very rapidly which provides it with a verysteep slope. This'peaked voltage or high voltage pipexists for a veryshort duration of time and does not appreciably increase the R. M. S.value of the sinusoidal voltage. This peaked voltage preferably has avalue of approximately 170 volts which is added to the amplitude of thevoltage supplied through lines 19 and 20 with the sum appearing acrosslamp 10 under; starting conditions. The amplitude and the steep wavefront of the peaked voltage is conducive to ionization of the gases inthe lamp 10. The high rate of voltage change of the steep wave front isparticularly conducive tov producing an instantaneous ionization of thegases. The peak voltage also declines at a very rapid rate afterreaching the peak value so that there is relatively little energy in thevoltage. Its function is to. provide a starting potential across theelectrodes of the lamp 10. The peaks occur on each half of thesinusoidal voltage wave and are uniform in amplitude. When the lamp isconducting a high are current the waveform of the voltage across thelamp changes to a rather irregular. periodic wave and the sharp peakvoltage is eliminated by virtue of regulation. As the arc current isreduced in value to lower the brilliance of the lamp the, impedance ofthe lamp increases with the decrease in ionization of the lamp.correspondingly the eifect ofregulation on. the peaking. is reduced andthe peak voltage. produced in. the. coil 21 increases and is added tothe, lowered voltage. across the lamp 10 and coil 21 thereby maintainingthe are through thev lamp.

The cores 26 and 31 are spaced from one another by non-magnetic members47, 48 secured to the cores so that the legs 29;, 32 are provided withnon-magnetic separation 38 to prevent the flux which passes through the.constricted leg' 29. and: threading coil 22 from having an, alternatepath through the legs. 33, 34, of core' 31 and thus vitiating the elfectof inducing a peakvoltage in coil 21. The core 31 preferably comprises1aminations of ferro-magnetic material.

The coil 21 serves two purposes. One purpose is as a current limitingmeans and the other purpose as a 4 starter means. As a current limitingmeans it functions as a reactor 01' ballast to create a voltage so thatthe voltage across the lamp 10 is a value in the range of to volts forconventional lamps. The other purpose is to create a starting voltage asdescribed in detail hereinbefore.

The coil 23 is coupled with the windings 4%, 4-1 which supply theelectrodes 13 and 14, respectively, with a steady alternating currentfor heating the cathodes.

The transformer 15 has windings 42 and 43. The coil 23 is connectedacross the winding 43 by the conductive wires 19 and 24 and is suppliedfrom the winding 43 with a steady alternating current. The coil 21 andlamp 113 are connected in series across the winding 42 and the winding43 through the slider 44. One end of the coil 21 is connected to theslider 44 slideably engaging the turns of the winding 42 and the otherend of the coil 21 is connected to the winding 43 through the line 20,lamp 10 and line 19, so that when the slider is at the terminal A end ofthe winding 42 the full voltage across the terminals 17, 18 is appliedacross the coil 21 and the electrodes 13 14- of the lamp 10, and whenthe slider is at the terminal B end the voltage of the winding 43 isimpressed across the coil 21, lamp 16. Thus the current supplied to thelamp 10 may be varied. The voltage across electrodes 13, 14 remainsgenerally constant and the voltage across the coil 21 changes inaccordance with the current or the changes of the voltage betweenterminal C and the slider 22. With a 48-inch, 40 watt lamp as an example230 volts are impressed across the terminals 17, 18. This voltage isapportioned across windings 42, 43 with winding 43 having a voltage ofapproximately 85 volts and the winding 43 has a voltage of volts. Thevoltage may be varied across the coil 21 and lamp 10 from 85 volts to230 volts.

When the slider 44 is at the terminal A end the lamp 10 is at fullbrilliance. As the slider is moved toward the terminal B end the voltageacross the coil 21 and lamp 10 is reduced and the current through thelamp 10 is correspondingly reduced. The energy that is sup plied to thearc is lessened and the radiation of the arc drops and therefore thefluorescent coating 12 does not receive suflicient radiation to hold itat full brilliance and the radiation correspondingly declines. Thus asthe voltage is reduced the radiation supplied to the coating 12 isreduced and over-all illumination declines. Conversely, as the currentis increased when the slider 4-4 is moved towards the terminal A end,more energy is supplied to the lamp and the radiation from thefluorescent coating correspondingly increases in intensity. At the lowerintensities when the tube would normally blackout, the high voltage peakoccurs across the electrodes 13 and 14 to refire the arc and maintainthe lamp illuminated. Even when the lamp is at its, lowest intensity thepeak voltage is applied across the electrodes 13, 14 to maintain thearc. Therefore the tube also starts at these low intensiies. The fullrange ofvoltage available across windings 42, 43 of the transformer 15is not needed to dim the lamp. The portion between terminal A andterminal B is sufficient to reduce the lamp to a dim-out condition.

The core 31 may be modified by reducing the crosssection. of the fluxpath through one of the legs of the core. For example, the leg 34 mayhave an opening 46. Such a magnetic constriction modifies the impedanceof the coil 21 and the core 31 with respect to the current level. Thesize and shape of the hole or constriction can be varied and the neteffect is to alter the normal impedance or B--H curve of the combinationof coil and core. The transformer 15 illustrates a typical source offixed and variable alternating voltage for the control system. Othertypes of variable and fixed A. C. supplies may be used with appropriatephase. relationships. A single autotransformer 15 may control aplurality of fluorescent lamps, the number of lamps depending upon therating of the autotransformer utilized.

The lines 50, 51, 52 may be extended to connect to other lamps andballasts such as the ballast shown in Fig. 1. Each lamp has a ballastsimilar to the one in Fig. 1 and is similarly connected.

It is thus seen from the above description that there are manyadvantages in the invention. It is capable of starting at any point ordegree of illumination. The starting circuit is built into the ballastlimiting the current through the lamp and does not have any movableelements that require replacement. Smooth dimming can be obtained over awide range of lamp intensities without the necessity of extensive andcomplicated equipment. The only additional piece of equipment requiredis an adjustable transformer.

Small condensers 47 and 48 are connected across the electrodes 13, 14and the coil 21, respectively, for the purpose of suppressing radiointerference and reduce striations in the luminous column of thefluorescent lamp.

Although the invention has been described as varying the intensity ofillumination of a particular fluorescent lamp, it may also be adapted tovary the radiation of similar gaseous discharge lamps such asultraviolet lamps and other types of fluorescent lamps.

Various other modifications and changes may be made without departingfrom the scope of the invention as set forth in the appended claims.

I claim:

1. Apparatus for starting a gaseous discharge lamp comprisingelectromagnetic means adapted to be connected in series with a gaseousdischarge lamp to limit the arc current therethrough and electromagneticmeans for producing high voltage pips of short duration in said firstmeans for starting a gaseous discharge lamp.

2. Apparatus for adjusting the intensity of illumination of a gaseousdischarge lamp comprising means adapted to be connected in series with agaseous discharge lamp to limit the arc current therethrough, meanscoupled with said first means for producing high voltage pips of shortduration in said first means for starting a gaseous discharge lamp, andvoltage adjusting means for connection across said first means and agaseous discharge lamp to vary the potential thereacross for dimming thelamp.

3. A circuit for adjusting the intensity of illumination of afluorescent gaseous discharge lamp comprising a gaseous discharge lamp,a ballast in series with said lamp, means for forming high voltage pipsof short duration in said ballast for igniting said lamp and means forsupplying a voltage adjustable over a range connected across saidballast and said lamp to vary the intensity of illumination of saidlamp. v

4. A laminated ferromagnetic core with a portion having a highpermeability at low flux values and saturating at higher flux values,means for supplying an alternating flux to said core, a secondferromagnetic core having a winding around said second core and saidportion to couple said flux of said portion with said coil to producehigh voltage pips of short duration in said winding on creation of analternating flux in said first core.

5. A starting ballast for a gaseous discharge lamp comprising alaminated ferromagnetic core having a constricted leg, a second leghaving a permeability lower than said first leg at low flux values and athird leg, a first coil wound around said third legfor providingelectromagnetic flux to said constricted leg to saturate said leg at lowflux values, a second laminated ferromagnetic core magneticallyseparated from said constricted leg, a second coil wound around saidsecond core and said constricted leg to provide an impedance limitingcurrent therethrough and creating high voltage pips of short durationacross the output of said second coil.

6. Apparatus for starting a gaseous discharge lamp and adjusting theintensity of illumination comprising a laminated ferromagnetic corehaving a constricted leg, a

second leg having a permeability lower than said first leg at low fluxvalues and a third leg, a first coil wound around said third leg forproviding electromagnetic flux to said constricted leg at low fluxvalues, a second laminated ferromagnetic'core spaced from saidconstricted leg, a second coil for connection in series with a gaseousdischarge lamp and wound around said second core and said constrictedleg to provide an impedance for limiting the arc current through agaseous discharge lamp and creating high voltage pips of short durationfor starting a gaseous discharge lamp and a variable transformer forconnection across a gaseous discharge lamp and said second coil inseries for varying the potential thereacross.

7. Apparatus as claimed in'claim 6 wherein said second core has a legwith a constriction therein.

8. Apparatus for-starting a gaseous discharge lamp comprising meansadapted to be connected in series with a gaseous discharge lamp to limitthe arc current therethrough and means having a separate electromagneticiron core spaced from said first means, said first means coupled withmagnetic flux through said means for producing high voltage pips ofshort duration in said first means and for starting a gaseous dischargelamp.

9. Apparatus for starting and maintaining the ionization of a gaseousdischarge lamp over a range of voltages applied for controlling theintensity of illumination of the lamp and comprising a reactor core anda winding around said core for passing current to a gaseous dischargelamp and having an impedance limiting the maximum current passingthrough the Winding, reactor means having a first flux path of highpermeability and a second flux path of a reluctance higher than thefirst flux path and a higher flux capacity, means for supplying flux tosaid paths, said first flux path passing through said first Winding andmagnetically separate from said reactor core, said first flux pathhaving a low flux capacity and rapidly saturating to create a highvoltage pip of short duration additively superimposed on the alternatingcurrent across a discharge lamp to start and maintain the ionization ofa gaseous discharge lamp.

10. Apparatus for starting and maintaining the ionization of a gaseousdischarge lamp over a range of voltages applied for controlling theillumination of the lamp and comprising reactor means having a windingadapted to be connected in series with a gaseous discharge lamp to limitthe maximum alternating current therethrough, a second reactor meanshaving a high permeability and a low flux capacity fiuX path and asecond flux path having a higher flux capacity and a higher reluctancethan said first path, a winding coupled to both of said paths andcreating a flux therein, said first path coupled through the winding ofsaid reactor means to produce high voltage pips of short duration insaid reactor winding and said second means passing the remainder of theflux of said second winding, the alternating voltage applied to I saidfirst winding and said voltage pip being in timed relation so that saidvoltage pip is additively superimposed on each half cycle of the voltageacross the lamp to produce a total voltage suificient to ionize agaseous discharge lamp.

11. Apparatus for starting and maintaining the ionization of a gaseousdischarge lamp and comprising a ferromagnetic core and a winding forminga reactor for having an impedance limiting the current supplied to agaseous discharge lamp, a second ferromagnetic means having one fluxpath of a high permeability and low flux capacity, and a second parallelflux path having a higher reluctance and a higher flux capacity thansaid first flux path, a

winding coupled to said first and second flux paths to provide fluxthereto and said first flux path passing through said first winding tocreate a sharp voltage pip of short duration in said first winding intimed relation with the alternating voltage applied to said winding tosuperimpose said voltage pip of short duration on said applied voltageto create a voltage sufiicient to ionize a gaseous discharge lamp.

12. Apparatus for starting and maintaining the ionization of a gaseousdischarge lamp and comprising a reactor core and a Winding around saidcore for passing alternating current to a gaseous discharge lamp andhaving an impedance that varies inversely to the current through thelamp and having a value limiting the maximum current passing through theWinding, reactor means having a first flux path of high permeability andlow flux capacity and a second flux path of a reluctance higher than thefirst flux path and with a higher flux capacity, means for supplyingflux to said paths to pass the flux through the first flux path, saidfirst flux path passing through said first Winding and magneticallyspaced from said ferromagnetic core to create a voltage of shortduration additive to each half cycle of the alternating voltage across agaseous discharge lamp and increasing in value as the current throughsaid Winding decreases so that the total voltage is sufficient to ionizethe discharge lamp.

References Cited in the file of this patent UNITED STATES PATENTS1,835,209 Dowling Dec. 8, 1931 2,298,589 Reitherrnan et a1. Oct. 13,1942 2,598,617 Stirnler May 27, 1952 2,650,326 Williams Aug. 25, 19532,665,394 Arvidsson et a1. Jan. 5, 1954 U. S. DEPARTMENT OF COMMERCEPATENT OFFICE CERTIFICATE OF CORRECTION Patent Non 2,821,661 January 28,1958 Arthur Lo Bastian It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionand that the said Letters Patent should read as corrected below.

(301mm 1, line 31, for "dependent of" read dependent on line 57.5, for"reversal of" read reversal or column 2, line 44, for "13 and 14" read13 and 14 are w line 47, for -"activity" read activated line 56, for'hazs a range" read have a range column 3, line 5, for

"and that the read and the column 4, line 22, for "electrodes l3 14"read electrodes 13, 14 column 5, line 46, strike out "fluorescent"Signed and sealed this 18th day of March 1958.,

(SEAL) Atteet:

KARL Ho AXLINE ROBERT C. WATSON Atteeting Officer Cunnissioner ofPatents 1 U. S. DEPARTMENT OF COMMERCE PATENT OFFICE CERTIFICATE OFCORRECTION Patent Noo 2,821,661 January 28, 1958 Arthur L,, Bastian Itis hereby certified that error appears. in the printed specification ofthe above numbered patent requiring correction and that the said LettersPatent should read as corrected below.

Column 1, line 31, for "dependent of" read dependent on line 5.5, for"reversal of" read 1- reversal or column 2, line 44, for "13 and 14"read l3 and lAYare line 47, for "activity" read activated =5 line 56,for fihas a range" read have a range column 3, line 5 for "and that theread and the column 4, line 22, for "electrodes l3 14" read meelectrodes l3, 14 as; column 5, line 46, strike out "f.l1.1orescentSigned and sealed this 18th day of March 1958,

(SEAL) Attest:

KARL AXLINE ROBERT c. WATSON Atteeting Officer Commissioner of Patents

